1. Field of the Invention
The present invention generally relates to a thermal barrier coating that is excellent in the durability and a manufacturing method thereof and specifically relates to a construction of a ceramics layer used as a top coat of the thermal barrier coating. The present invention also relates to a turbine part using this thermal barrier coating and a gas turbine using this turbine part.
2. Description of the Prior Art
Recently, enhancement of the thermal efficiency of thermal power generation is being studied as one of energy saving measure. For enhancing the efficiency of a power generation gas turbine, elevating the gas inlet temperature is effective, and the temperature thereof sometimes becomes as high as about 1500° C. In order to realize such a high temperature of a power generation plant, it is necessary to use heat resistant parts and components in constructing stationary blades, moving blades, combustor walls, etc. constituting the gas turbine. While the turbine blades are made of heat resistant metals, they can still hardly resist such a high temperature. Hence, in order to ensure protection from the high temperature, to form a thermal barrier coating or TBC is currently being carried out such that a ceramics layer of oxide ceramics is formed on a base material of heat resistant metal via a metallic bond layer by a coating process of thermal spraying, etc. As the ceramics layer, a material of ZrO2 group, specifically YSZ (yttria stabilized zirconia), which is ZrO2 partially or completely stabilized by Y2O3, is often used, as it has a relatively low thermal conductivity and relatively high thermal expansion coefficient in the ceramics materials.
Even in the case where the gas turbine moving blades or stationary blades are coated with the thermal barrier coating having the ceramics layer of the above-mentioned YSZ, however, it is considered that the gas turbine inlet temperature is elevated to a temperature exceeding 1500° C. according to the kind of gas turbine. If operation is at such a high temperature, there is a risk that a portion of the ceramics layer peels off during the gas turbine operation under severe operating conditions, damaging the heat resisting ability.
Also, from the viewpoint of recent environmental protection measures, development of a closed type gas turbine that is able to correspond to a recovery of carbon dioxide is being carried out. In this type of gas turbine, the turbine inlet temperature is considered to become as high as 1700° C. and a surface temperature of the turbine blade is presumed to become as high as 1300° C. Thus, a higher heat resisting ability is being desired for the thermal barrier coating of the turbine blade.